When an electronic calculator is first turned on and power is supplied to its memory and computational circuits, it is usually necessary to clear random bits out of the memory before the calculator is ready to use. Thus, in prior art programmable calculators, a power-on or turn-on program is usually provided to clear all memory registers and insure that the calculator is ready for the first computation. Some programmable calculators have one or more keys on the keyboard which, when depressed, will initiate the performance of a subroutine which the user may define in the calculator memory. These user-definable keys provide a time saving feature for users who have frequently used subroutines comprising a number of calculator functions that require the sequential operation of a number of keys to perform. For example, the calculator keyboard may provide keys enabling the user to perform simple mathematical functions such as add, subtract, multiply, divide, square root, and so forth. A user may desire to perform a more complex function on a repeated basis such as the variance or standard deviation of data he is analyzing. User-definable keys allow the user to program these subroutines into memory and perform the desired operation on entered data with the depression of a single key. In the past it was necessary to redefine the functions associated with user-definable keys each time the calculator was turned on, since the turn-on program would clear the memory associated with the user-definable keys along with other parts of the calculator memory.
According to the preferred embodiment of the present invention, a calculator having user-definable keys is provided with a routine in its turn-on program which predefines the user-definable keys with commonly used functions. Thus, these keys are immediately usable by the user after the calculator is turned on, without having to program the memory associated with the keys. However, if the user desires to have other functions associated with the user-definable keys he may reprogram the keys with as much ease as user-definable keys were programmed in prior art calculators. The user-definable keys may be predefined with functions normally accessible from the keyboard or with functions that are stored in a read-only memory or other hardware in the calculator, but are not normally accessible from the keyboard.